Some government operations have historically depended upon the element of surprise, but modern operations often require two-way data transmissions among operating units. Such transmissions if detected can reveal the location of the transmitter. If the transmissions can be decoded, other important information may be compromised. It is therefore important to prevent detection or localization of personnel and vehicles by monitoring of their electromagnetic data transmissions. Many techniques have been advanced to make interception of communications difficult. For example, spread-spectrum techniques such as frequency hopping and direct sequence spreading reduce the average transmitted power in a given bandwidth to make interception difficult. The phase of a carrier can be randomized as described in U.S. patent application Ser. No. 724,309 filed Apr. 12, 1985, now U.S. Pat. No. 4,652,838 in the name of Nossen, to reduce the detected power density. It is often desirable to combine two or more communication techniques in order to further increase the difficulty of receiving a transmitted signal or of decoding the information contained therein. Thus, it is advantageous to have many techniques for preventing the reception of transmissions, for preventing the decoding of the information contained therein if the transmissions are received, or both.